On the prediction of settling velocity for plastic particles of different shapes

Transport processes of plastic particles in freshwater and marine environments are one of the relevant advances of knowledge in predicting the fate of plastic in the environment. Here, we investigated the effect of different shapes on the settling velocity, finding a representative reference diameter which encompasses three-dimensional shapes like pellets or spherules, two-dimensional shapes like fragments or disks, and one-dimensional shapes like filaments or fibers. The new method is able to predict the settling velocity of plastic and natural particles given the representative size and the Corey shape factor coefficient, over the entire range of viscous to turbulent flow regime. The calibration of the method with experimental data, and the validation with an independent dataset, support its application in a wide range of hydraulic conditions. [Display omitted] •Joint effect of shape and representative size on particle fall velocity is examined.•The proposed reference diameter encompasses all 1D, 2D and 3D shapes.•Experimental velocity of both 2D and 3D shapes are well predicted by this approach.•The method for estimating settling velocity applies to a wide range of flow regimes.